Apex domains cannot have CNAME records.
Question and response
Question
dig 203.194.in-addr.arpa. NS
Answer
203.194.in-addr.arpa. 5 NS auth0020.ns.eu.uu.net.
203.194.in-addr.arpa. 5 NS auth0030.ns.eu.uu.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0